The issue is that when I open HWiNFO sensors, PSU fan (RM750i) is stopped to 0 RPM. I can disable CorsairLink support in settings to prevent that from happening, but that would prevent from being able to monitor PSU power usage when gaming through OSD.
Corsair Link is not installed, I use SIV64 (http://rh-software.com/) to enable fixed fan speed, the issue persists even if SIV64 is not running, the only way for the fan to work is to start SIV64 after HWiNFO has been started. I realize there are issues with the protocol used to communicate with the PSU, but the thing is, I've tried two other monitoring software, AIDA64 and HWmonitor, which are capable of monitoring corsair PSU, and these have no issues, when you open their sensors, the fan is still running. So I think if AIDA64 and HWmonitor can get PSU stats without stopping the fan, then there is something HWiNFO does that makes the fan to stop.
When fan is stopped by HWiNFO, SIV64 shows PSU fan control mode to "PSU Default", so what seems to be happening is that when HWiNFO is reading PSU stats, fan control settings previously saved are erased and fan control reverts to stock Default settings, which involves semifanless operation (0 RPM) when you are below certain load and temperature.